Ask Bill about carbing a DeLorean and other K-Jet/Carb tangets

[stevedmc]

I've got my bowl of popcorn and am ready for some good reading.

[DCUK Martin]

I see no Bill in the membership list?

[DMCMW Dave]

Maybe nobody told him about the .org thing. . . . .

[stevedmc]

I wonder what happened to theAviator. He was getting ready to convert a few months back.

[The Aviator]

we're back!!!

[The Aviator]

I wonder what happened to theAviator. He was getting ready to convert a few months back.

i was checking everyday to see if there was any updates, i than threw a google search found a dmchelp.com thread about dmctalk going now, checked that daily to find us with a new name, glad they worked everything out, i was kicking myself in the ass because i didnt have bills contact info

danny

[stevedmc]

Shoot me a PM. I believe I have both his phone number and email addy.

[A Van]

A clean with a scourer as washing up liquid, followed by a respect ought to sort it

[content22207]

I am starting to receive PM inquiries that indicate a general "theory of carburetion" post would be appropriate (there's one on the old site, but those archives are slow to migrate over here):

To combust properly in the cylinders, gasoline and air must be mixed in appropriate quantities. The gasoline also needs to be atomized into fine droplets -- liquid gasoline does not combust very well.

For purposes of this post, "carburetor" refers to the Autolite/Motorcraft 2100/2150 2 barrel carburetor in particular.

A carburetor uses air flow into the engine to draw the proper amount of gasoline into the air stream and atomize it. That is the only thing the driver controls -- air flow into the engine (via the throttle plates). Gasoline delivery is automatic, using physical properties of fluid dynamics alone.

As air flows into the engine, it passes through restrictions known as venturis. The venturis are shaped like a section of garden hose pinched between your fingers (the pinch is 360 degrees around). As air passes through the venturis, it speeds up, reducing its pressure in the process -- air inside the venturis has lower pressure than air around any other part of the carburetor.

The venturis are connected to a small supply of gasoline in a little tank known as the bowl. Because air around the bowl has higher pressure than air in the venturis, gasoline is pushed from the bowl to the venturis. Small holes in the venturis atomize the gasoline as it leaves them and enters the air steam into the engine.

Opening the throttle plates increases air flow into the engine, further reducing air pressure in the venturis. As the pressure differential between the venturis and the bowl increases, increased amounts of gasoline are pushed into them. The converse happens when the throttle plates are closed. This is how a carburetor meters fuel for varying amounts of throttle (varying amounts of air).

The amount of fuel that leaves the bowl to the venturis is metered by holes known as "jets." Smaller jets allow less fuel to leave the bowl than larger jets do. To change overall air/fuel ratios, the jets are physically removed and replaced with different sizes.

That is the essence of carburetion.

The addition of a choke plate before the throttle plates allows more fuel to be drafted for any given amount of throttle plate opening. The choke plate restricts air flow into the engine. Because the size of the combustion chambers is unchanged, the volume of air drawn into them is the same, but reduced flow permitted by the choke plate causes that air to have lower pressure than it would have otherwise. Lower pressure than otherwise in the venturis leads to more gasoline than otherwise being pushed into the air stream. When the choke plate is mostly closed, gasoline flow through the venturis is at its richest. As the choke plate opens, gasoline flow through the venturis (relative to air flow metered by by the throttle plates) leans out. When the choke plate is fully open, gasoline flow through the venturis is at its leanest.

On a 2100, choke plate movement is typically automated. Early models used exhaust temperature to heat up a spring attached to the choke plate, gradually opening it. Later models passed electricity through the spring to heat it.

Because gasoline is heavier than air, rapid increases in air flow into the engine will cause the air/fuel mixture to go lean (gasoline being pushed out of the bowl takes longer to catch up to the air). To compensate, there is a little pump attached to the throttle mechanism. Small amounts of throttle movement will inject small amounts of fuel from this pump into the air stream. Large amounts of throttle movement will inject large amounts of fuel from this pump into the air stream. The pump only activates one time for each throttle plate movement.

And that is pretty much it. A carburetor uses air flow into the engine alone to meter its fuel. As long as there is fuel in the bowl, and as long as all air being drawn into the engine passes through the venturis, you will have appropriate fuel delivery.

Bill Robertson
#5939

[Farrar]

I am starting to receive PM inquiries that indicate a general "theory of carburetion" post would be appropriate

Would you like for me to post that document I typed up?

Farrar